Field of the Disclosure
The present disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of effectively improving response speed and transmittance.
Description of the Background
In general, a liquid crystal display device (LCD) is driven by using optical anisotropy and polarization properties of liquid crystal. Since the liquid crystal has a long and thin structure, liquid crystal molecules have an alignment direction. The alignment direction of the liquid crystal molecules may be controlled by applying an electric field to the liquid crystal.
Therefore, when the alignment direction of the liquid crystal molecules is arbitrarily adjusted, an alignment of the liquid crystal molecules may be changed. Accordingly, light may be refracted in the alignment direction of the liquid crystal molecules due to the optical anisotropy to display image information.
Currently, an active matrix LCD (hereinafter, abbreviated as LCD), in which thin film transistors and pixel electrodes connected to the thin film transistors are arranged in a matrix form, has been attracting the most attention due to high resolution and superiority in displaying moving images.
The LCD includes a color filter substrate on which a common electrode is formed, an array substrate on which a pixel electrode is formed, and liquid crystal interposed between the two substrates. Since the liquid crystal is driven by an electric field induced between the common electrode and the pixel electrode, the LCD has excellent characteristics such as high transmittance and aperture ratio.
In addition, recently, an in-plane switching (IPS) mode LCD, in which electrodes have been alternately disposed on one substrate of upper and lower substrates and liquid crystal is disposed between the upper and lower substrates to display an image, has been developed.
Commonly, the IPS mode LCD displays an image by adjusting light transmittance of liquid crystal having dielectric anisotropy (Δε) by using an electric field. The IPS mode LCD is mostly formed by attaching a color filter substrate on which a color filter is formed and an array substrate on which a thin film transistor is formed and interposing liquid crystal therebetween.
Here, the array substrate includes a thin film transistor, a pixel electrode, and a common electrode, which are formed in each pixel region defined on the array substrate by a crossing of a gate line and a data line.
The thin film transistor supplies a data signal from the data line to the pixel electrode in response to a gate signal from the gate line.
The pixel electrode receives the data signal from the thin film transistor to allow liquid crystal to be driven, and the common electrode receives a common voltage which is a reference when the liquid crystal is driven. The liquid crystal is rotated according to an electric field generated by the data signal of the pixel electrode and the common voltage of the common electrode, so that light transmittance is adjusted to implement gray scales.
Recently, a fringe field switching (FFS) mode LCD having a better viewing angle characteristic than that of the IPS mode LCD has been proposed.
FIG. 1 is a schematic view showing the related art FFS mode LCD.
As shown in FIG. 1, the FFS mode LCD 10 includes a gate line 43 having a linear shape in one direction and a data line 51 having a linear shape crossing the gate line 43 to define a pixel region P.
In addition, a switching element, i.e., a thin film transistor Tr is formed in the pixel region P. The thin film transistor Tr is connected to the data line 51 and the gate line 43 and includes a gate electrode (not shown), a gate insulating layer (not shown), a semiconductor layer (not shown), and source and drain electrodes 55 and 58.
A plate-shaped common electrode 60 and a pixel electrode 70 overlapping the plate-shaped common electrode 60 are formed in the pixel region P. The pixel electrode 70 has a plurality of bar-shaped openings.
In this case, the plate-shaped common electrode 60 is formed on the entire surface of a display region, but a portion of the plate-shaped common electrode 60 corresponding to one pixel region P is indicated by a dotted line.
The FFS mode LCD 10 having such a configuration generates a fringe field by applying a voltage to the plate-shaped common electrode 60 and the pixel electrode 70 having the plurality of bar-shaped openings in each pixel region P.
Meanwhile, recently, in order to enhance the realism of a display, high response speed of an LCD has been actively researched.
Here, the response speed (hereinafter, referred to as GTG (grey to grey)) indicates the time it takes to go from a light gray color to a dark gray color. That is, the response speed is a value obtained by measuring a time for brightness to be changed from 10% to 90%.
For example, in the case of a virtual reality (VR) device, since an image is viewed in a state in which eyes are close to a screen, high response speed of an LCD becomes very important.
However, since the FFS mode LCD 10 uses an electro-optical effect of a fluid, i.e., liquid crystal, response speed is limited due to behavior of the liquid crystal. Therefore, an afterimage due to flickering can occur. In the case of the related art FFS mode LCD 10, a viewing angle characteristic is improved, but there is a limit in improvement of response speed.